The family house was small: three rooms, a tiny kitchen and bathroom, built of poor-quality concrete bricks with a corrugated asbestos roof, in block four of Jabalia refugee camp in northern Gaza. There are hundreds of similar homes crammed into the overcrowded streets, filled with some of the poorest and most vulnerable families in the Gaza Strip.

But it was this house, where Anwar and Samira Balousha lived with their nine children, that had the misfortune to be built next to what became late on Sunday night another target in Israel's devastating bombing campaign of Gaza.

An Israeli bomb struck the refugee camp's Imad Aqil mosque around midnight, destroying the building and collapsing several shops and a pharmacy nearby. The force of the blast was so massive it also brought down the Balousha family's house, which yesterday lay in ruins. The seven eldest girls were asleep together on mattresses in one bedroom and they bore the brunt of the explosion. Five were killed where they lay: Tahrir, 17, Ikram 15, Samer, 13, Dina, eight and Jawahar, four.

They were the latest in a growing number of civilian casualties in Israel's bombing campaign. At least 335 Palestinians have been killed and as many as 1,400 injured. On the Israeli side, four people have been killed by Palestinian rockets. Israel's military offensive continues and may yet intensify.

Imam, 16, lay in the room with her sisters but by chance survived with only injuries to her legs. She was eventually pulled free and rushed to hospital. "I was asleep. I didn't hear anything of the explosion," she said yesterday as she sat comforting her mother. "I just woke when the bricks fell on me. I saw all my sisters around me and I couldn't move. No one could see me from above. The neighbours and ambulance men couldn't see us. They were walking on the bricks above us. I started to scream and told my sisters we would die. We all screamed: 'Baba, Mama. Come to help us.'"

Her parents had been sleeping in the room next door with their two youngest children, Muhammad, one, and Bara'a, 12 days.

Their room was damaged and all were hurt, but they survived and were taken straight to hospital even before any of the older girls were found.

Imam eventually recognised her uncle's voice among the rescuers and she shouted again for help. "He found me and started to remove the bricks and the rubble from me," she said. "They started to pull me by my hands, the bricks were still lying on my legs."

Her mother, Samira, 36, had seen the pile of bricks in the girls' bedroom and was stricken with grief, convinced they were all dead. Like all the family, she was asleep when the bomb struck. "I opened my eyes and saw bricks all over my body," she said. "My face was covered with the concrete blocks."

She checked on her two youngest children and then looked in the room next door. "I didn't see any of my daughters, just a pile of bricks and parts of the roof. Everyone told me my daughters were alive, but I knew they were gone."

She sat on a sofa surrounded by other women at a neighbour's house further along the street and struggled to speak, pausing for long moments and still overcome with shock.

"I hope the Palestinian military wings retaliate and take revenge with operations inside Israel. I ask God to take revenge on them," she said.

Her husband, Anwar, 40, sat in another house where a mourning tent had been set up. He was pale and still suffering from serious injuries to his head, his shoulder and his hands. But like many other patients in Gaza he had been made to leave an overcrowded hospital to make way for the dying. Yesterday his house was a pile of rubble: collapsed walls and the occasional piece of furniture exposed to the sky. He spoke bitterly of his daughters' deaths. "We are civilians. I don't belong to any faction, I don't support Fatah or Hamas, I'm just a Palestinian. They are punishing us all, civilians and militants. What is the guilt of the civilian?" Like many men in Gaza, Anwar has no job, and like all in the camp he relies on food handouts from the UN and other charity support to survive.

"If the dead here were Israelis, you would see the whole world condemning and responding. But why is no one condemning this action? Aren't we human beings?" he said. "We are living in our land, we didn't take it from the Israelis. We are fighting for our rights. One day we will get them back."